Switched-mode power converters perform the power conversion by periodically storing and releasing energy within reactive components. This process of periodically storing and releasing energy is controlled by power switches. The most common power converter topologies, like e.g. buck converters, boost converters, buck-boost converters, full-bridge converters store the energy within an inductor, i.e. they provide energy storage in the magnetic field originating from the current flowing through the winding of the inductor.
During the energy-storage phase, the inductor current increases approximately linearly, whereas it decreases also approximately linearly during the energy-release phase. In order to simplify the design and the control of these converters, the inductor is often dimensioned so that at the end of the energy-release phase, the inductor current is still higher than zero. Thus, as a consequence, the inductor is never completely discharged. This is known as continuous conduction mode, CCM.
If the power consumed by the load decreases, the average value of the inductor current reduces and thus the minimum value of the inductor current approaches to zero. In power converters synthesized with unidirectional power switches, for instance diodes, the inductor current cannot reverse. Consequently, if the inductor current reaches zero during the energy-release phase, because of the unidirectional switches, it will remain zero until the switches are activated again (energy-storage phase). This is known as discontinuous conduction mode, DCM.
DE GUSSEME K ET AL: “Sample correction for digitally controlled boost PFC converters operating in both CCM and DCM”, APEC 2003. 18TH. ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION. MIAMI BEACH, Fla., Feb. 9-13, 2003; [ANNUAL APPLIED POWER ELECTRONICS CONFERENCE], NEW YORK, N.Y.: IEEE, US, 9 Feb. 2003 (2003-02-09), pages 389-395 vol. 1 discloses a digitally controlled boost PFC converter operating in both CCM and DCM and a study of the input current distortion caused by the sampling algorithm. A correction factor is derived to compensate for the error on the input current samples. The theoretical results are verified experimentally.